receptors Flashcards
Describe the basic structure of a Pacinian corpuscle
Describe how a generator potential is established in a Pacinian corpuscle
- Mechanical stimulus eg. pressure deforms lamellae and stretch- mediated sodium ion (Na+) channels
- So Na+ channels in membrane open and Na+ diffuse into sensory neurone
○ Greater pressure causes more Na+ channels to open and more Na+ to enter - This causes depolarisation, leading to a generator potential
○ If generator potential reaches threshold it triggers an action potential
Explain what the Pacinian corpuscle illustrates
● Receptors respond only to specific stimuli
○ Pacinian corpuscle only responds to mechanical pressure
● Stimulation of a receptor leads to the establishment of a generator potential
○ When threshold is reached, action potential sent (all-or-nothing principle)
Explain the differences in sensitivity to light for rods & cones in the retina
Rods are more sensitive to light
- Several rods connected to a single neurone
- Spatial summation to reach / overcome threshold (as enough neurotransmitter released) to generate an action potential
Cones are less sensitive to light
● Each cone connected to a single neurone
● No spatial summation
Explain the differences in visual acuity for rods & cones in the retina
Rods give lower visual acuity
● Several rods connected to a single neurone
● So several rods send a single set of impulses to brain (so can’t distinguish between separate sources of light)
Cones give higher visual acuity
● Each cone connected to a single neurone
● Cones send separate (sets of) impulses to brain (so can distinguish between 2 separate sources of light)
Explain the differences in sensitivity to colour for rods & cones in the retina
Rods allow monochromatic vision
● 1 type of rod / 1 pigment
Cones allow colour vision
● 3 types of cones - red-, green- and blue-sensitive
● With different optical pigments → absorb different wavelengths
● Stimulating different combinations of cones gives range of colour perception
